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In January, the Food and Drug Administration approved Kalydeco, the first drug to actually reverse the biological changes that cause the lung-destroying disease. The pill improves lung function, helps patients gain weight, and makes them feel better. (See my magazine piece on it from last year.)

The problem with Kalydeco, aside from its $294,000 per patient per year cost, is this: it only works for 4% of cystic fibrosis patients, or about 1,200 people. The other 28,800 or so people with cystic fibrosis are out of luck. Unless, that is, Vertex can make good on its promise to make a second drug which makes Kalydeco effective in some of these patients.

The idea is this: Kalydeco works by improving the function of the Cystic Fibrosis Transmembrane Regulator protein. But this CFTR protein is buried deep inside cells in most CF patients. So the idea is to use a second pill to get the CFTR protein up to the cell surface so Kalydeco can work. The first test of such a compound, VX-809, was unveiled in May, with signs of efficacy and plans on Vertex's part to proceed into larger trials. Within a month, Vertex had corrected its data, saying that it had confused relative improvements (percentages) and absolute ones (the endpoint in question, FEV1, is given as a percent of expected lung function.) See "Clearing Up Vertex's Data Bungle" for more on that.

Today Vertex released more data from that study at a medical meeting in Orlando. The big question is whether the this combination is working, or whether what looks like efficacy is just noise. Which is why this slide, which shows the data for every patient in the study to received the 600 milligram dose of VX-809 both by itself (during a run-in phase) and with Kalydeco is the best argument so far that this combo is helpful to patients -- thought not as helpful as Kalydeco is to those who can get that drug alone.

Note that how well patients do varies pretty wildly. And one thing that makes me concerned is that during the test of just VX-809, there is a lot more variability in the placebo group than in those getting VX-809. But it's hard to look at that plot on the right and not think that something is happening. Nobody in the group that got the drug combination did anywhere near as badly as the worst patients in the placebo group; nobody who received placebo did anywhere near as well as those who did best on the combo. It's understandable that Vertex decided to go into late-stage studies based on this data.

There were three doses of VX-809 used, too, and the drug seems to get more convincing as higher doses are used.

Not that there aren't some big caveats. For one thing, the fact that changes in sweat chloride, which should be evidence of the effectiveness of the drug combo, are not significant is a concern. More than that, I don't really see how anybody can be confident about how effective this combination is. As Mark Schoenebaum of ISI Group put it in a note to clients, "the magnitude of that activity is difficult (if not impossible) to ascertain" because of the small number of patients studied. So We'll have to wait for more data. But this does seem to validate both Vertex's decision to develop this combination therapy and a second one, and the decision to move into larger studies.